Listen. Find the value of $x$ in the equation $13-x=21$.
Answer (1)
Subtract 13 from both sides of the equation: 13 − x − 13 = 21 − 13 .
Simplify the equation: − x = 8 .
Multiply both sides by -1: x = − 8 .
The value of x is − 8 .
Explanation
Understanding the problem We are given the equation 13 − x = 21 and we want to find the value of x .
Subtracting 13 from both sides To isolate x , we first subtract 13 from both sides of the equation: 13 − x − 13 = 21 − 13
Simplifying the equation Simplifying the equation, we get: − x = 8
Multiplying by -1 Now, we multiply both sides of the equation by -1 to solve for x :
( − 1 ) ( − x ) = ( − 1 ) ( 8 ) x = − 8
Final Answer Therefore, the value of x is -8.
Examples
In real life, this type of equation can be used to determine how much something has changed. For example, if you started with $13 and ended up with 21 a f t ers p e n d in g so m e m o n ey ( x$), you can use the equation 13 − x = 21 to find out how much money you spent. Solving this equation tells you that you spent $8 (x = -8, meaning you spent $8).
