Question

5a(2x–a)–(8a–x)(2x–a)

Answer 1

Remember foil and distributive property
note the invible -1

5a(2x-1)-1(8a-x)(2x-a)
look at first bit
5a(2x-a)=10ax-5a^2
2nd part

-1(8a-x)(2x-a)
-1(16ax-2x^2-8a^2+ax)
-1(17ax-2x^2-8a^2)
-17ax+2x^2+8a^2

now combine the 2 parts
10ax-5a^2-17ax+2x^2+8a^2
2x^2+3a^2-7ax