Question

If m^2 + n^2 = 18 and mn=7, what is (m-n)^2

Answer 1

(m-n)^2 = m^2 - 2mn + n^2

(m-n)^2 = m^2 + n^2 - 2mn

Substitute m^2 + n^2 = 18 and mn=7

(m-n)^2 =18 - 2(7)

(m-n)^2 = 18 - 14

(m-n)^2 = 4

Answer 2

(m - n)^2 = 4

Explanation:

(m - n) ^2 = m^2 - 2mn + n^2 when (m-n)^2 is expanded using foil.

But m^2 + n^2 = 18 Given

mn = 7 Given

(m - n)^2 = m^2 + n^2 - 2 mn Substitute in the given values

(m - n)^2= 18 - 2*7 Reduce

(m - n)^2 = 18 - 14 Combine

(m - n)^2 = 4