Steel is a material that has low resistance to corrosion when interacting with a corrosive environment. The application of natural extracts as green inhibitors is able to provide good performance in inhibiting corrosion of steel with high inhibition efficiency. Natural extracts that are effective and efficient as corrosion inhibitors on steel are those which in their compound structure contain heteroatom groups (such as O, N, S, P) and aromatic rings. This work provides an important comparative overview for the development of green inhibitor natural extracts in steel. The results of theoretical studies based on quantum mechanics with the DFT method at the atomic level based on molecular orbitals, chemical quantum parameters, and adsorption characteristics show results that are in accordance with experimental studies. The frontier molecular orbital (FMO) plot shows the distribution of electron density in the HOMO-LUMO region as a predictor of the active site of the inhibitor molecule interacting with the steel surface. Quantum chemical parameters such as ionization potential (I), electron affinity (A), absolute electronegativity (χ), hardness (η), softness (σ), fraction of electrons transferred (ΔN), electrophilicity (ɷ), and electron backdonation (ΔEback-donation) was calculated to obtain a correlation between the electronic properties of the inhibitor molecule and the corrosion inhibition potential. The results of the calculation of the quantum chemical parameters show the reactivity of the inhibitor molecule which has a very good potential to interactand bind strongly to the steel surface. This has the potential to make the inhibitor molecule have a high inhibition efficiency. Chemical adsorption and/or physical adsorption by forming complex compounds between inhibitor molecules and the steel surface are corrosion inhibition mechanisms to protect steel from a corrosive environment.The development of future studies should be able to display the mechanism of interaction and inhibition of inhibitor molecules in more detail and systematically at the atomic level on several metal surfaces such as Fe, Al, Cu, and others.

This study aims to determine the types and factors that cause student difficulties in solving reasoning problems on the absolute value material. This research is a type of qualitative descriptive. The subjects of this study were students of class X MIPA 5 SMAN 3 Surakarta in the 2019/2020 school year. Subjects were taken using a purposive sampling technique. The data collection technique used tests and interviews. Before the test is used, it is validated by an expert. Data analysis was carried out using data reduction, data presentation, and concluding. The results of this study indicate that the types of student difficulties are 1) fact difficulties, where the subject has difficulty in analyzing and linking the information from the questions with the questions in the questions. The difficulty of the subject is because the subject does not understand the problem and rarely does the problem in the form of a story; 2) Conceptual difficulty, where the subject has difficulty determining the limits of the two absolute value equations. In determining the limits on the absolute value equation, it is necessary to define absolute value. The difficulty of the subject is because the subject still does not understand the absolute value material; 3) skill difficulty, where the subject has difficulty performing algebraic operations in determining the value of x. The difficulty of the subject is because the subject is not careful in doing and checking the written answers again.

This study aims to determine the effect of applying the picture and picture method to improve the numeracy skills of grade II students at SD Negeri 01 Mamben Daya for the 2022/2023 academic year. The research subjects were grade II students at SD Negeri 01 Mamben Daya with a total of 31 students consisting of 17 boys and 14 girls. The results of this study indicate that the results of the evaluation using a written test in the form of multiple choices to find out the acquisition of students' numeracy skills are quite good, namely from the first cycle the results were 64%, which then increased by 20% so that the proportion of completeness in the second cycle became 84% with an average class cycle I of 64 which then increased in cycle II to 84. Thus the application of the picture and picture method to improve numeracy skills in class II students at SD Negeri 01 mamben daya for the 2022/2023 academic year can improve participants' numeracy skills educate.

This study aims to determine the contribution of self-confidence to the mathematical reasoning abilities of high school students. The method used in this research is a survey method with correlation and regression techniques. The research sample was 93 high school students in the city of Surakarta, Central Java, Indonesia, with different abilities. The instrument used in this study was a written test of mathematical reasoning abilities on absolute value material, as well as a set of self-confidence questionnaire statements. Data analysis of mathematical reasoning ability and self-confidence in this study is the Pearson correlation analysis and regression with the help of SPSS 16.0. The results of the research data analysis showed that there was a positive correlation between self-confidence and students' mathematical reasoning abilities. The contribution of self-confidence to mathematical reasoning ability was 13.1% in the medium category. Students who have good self-confidence will always think positively that they are confident in their abilities, can solve special problems that require reasoning, thereby significantly increasing their reasoning abilities.