Answer:

A. ( 5a + b ) ( 3a - 4b )

Step-by-step explanation:

\begin{gathered}( \: 5a \: + \: b \: ) \: ( \: 3a \: - \: 4b \: ) \\ = \: 15 {a}^{2} - \: 20ab \: + \: 3ab \: - 4 {b}^{2} \\ = 15 {a}^{2} - \: 17ab \: - 4 {b}^{2} \end{gathered}

(5a+b)(3a−4b)

=15a

2

−20ab+3ab−4b

2

=15a

2

−17ab−4b

2

First Step:

( 5a ) ( 3a ) = 15a²

( 5a ) ( -4b ) = -20ab

( b ) ( 3a ) = 3ab

( b ) ( -4b ) = -4b²

Second Step:

-20ab + 3ab

= -17ab

✓ The sign are not the same. { + and - }

✓ All you need to do is...Copy the sign of the biggest number and then subtract.

√ 20 is the biggest number and the sign is negative ( - ) so copy the sign.

-20ab + 3ab = -

Now subtract the numbers... 20 - 3 = 17

-20ab + 3ab = -17

Copy the variables...

-20ab + 3ab = -17ab

DONE!

By the way if your gonna type the squared just long press the number.

Have a great day! Ey! :)²