Mathematics
Substitution
In this Class 9 Mathematics topic, students learn how to replace a variable with a known number or algebraic expression and then simplify the result correctly. The topic builds understanding of substitution in algebraic expressions, formulas, and equations, including the careful use of brackets, signs, powers, and the order of operations. As part of the Common Questions chapter, it also helps students identify typical calculation errors and check whether their final answer is reasonable.
Topic overviewटॉपिक का परिचय
Concept revisionअवधारणाओं का पुनरावर्तन
If \(y=4\), what is the value of \(y^2\)?
\(y^2\) means \(y\times y\). Substituting \(y=4\), we get \(y^2=4^2=4\times4=16\).
If \(u=7\) and \(v=2\), what is the value of \(u-v\)?
Substituting the given values in \(u-v\) gives \(7-2=5\), so option B is correct. Option A results from addition, \(7+2=9\), option C results from multiplication, \(7\times2=14\), and option D is an incorrect subtraction.