Question

What is the first step in solving this system of equations by elimination? 5a + 3b = –9 2a – 5b = –16

A.

Subtract the two equations.
B.

Add the two equations.
C.

Solve for a.
D.

Multiply the first equation by 2 and the second by –5.

Answer 1

\(\large \begin{array}{llll}
5a + 3b = -9&{\color{red}{ \times 5}}\implies &25a\cancel{+15b}=-45\\
2a - 5b = -16&{\color{red}{ \times 3}}\implies &6a\cancel{-15b}=-48\\
\hline\\
&&31a\qquad \qquad=-93
\end{array}\)

then solve for "a"
once you find "a", substitute that on either equation and solve for "b"

notice the step, so how we "eliminated" the " b's "