Raj tried to solve the following system. 9 x minus y is equal to 15 2 x plus 8 y is equal to 28 Raj's Work 9 x minus y is equal to 15 negative y is equal to 15 minus 9 x y is equal to negative 15 plus 9 x 2 x plus 8 times open paren 15 plus 9 x close paren is equal to 28 2 x plus 120 plus 72 x is equal to 28 74 x plus 120 is equal to 28 74 x is equal to negative 92 x is equal to negative 46 over 37 9 times open paren negative 46 over 37 close paren minus y is equal to 15 negative 414 over 37 minus y is equal to 15 y is equal to negative 969 over 37 What error did Raj make?
Answer
A
Raj forgot the negative sign when substituting negative 15 plus 9 x for y .
B
Raj found the value of negative y instead of y .
C
Raj subtracted 120 from both sides when he solved for the value of x .
D
Raj forgot to multiply the value of x by 9 when solving for the value of y .
Explanation
From 9x − y = 15, subtract 9x to get −y = 15 − 9x. Multiplying both sides by −1 gives y = −15 + 9x. Raj then substituted 15 + 9x into the second equation, leaving out the negative sign on 15. So the error is that he forgot the negative sign when substituting for y.
AI-written and checked against the verified answer.