Question

Given that the two expression(r+ a)(r – 15) and r² – br-75 are indentical calculate the value of b​

Answer 1

b = 10

Explanation:

expand expression and compare like terms.

(r + a)(r - 15) ← expand using FOIL

= r² - 15r + ar - 15a ← factor out r from second/ third terms

= r² + r(a - 15) - 15a

compare with r² - br - 75

then

- 15a = - 75 ( divide both sides by - 15 )

a = 5

and

a - 15 = - b ← substitute a = 5

5 - 15 = - b

- 10 = - b ( multiply both sides by - 1 )

10 = b