Question

how -9(a+b) = -3{(2a+b)+(a+2b)}

Answer 1

-9(a+b) = -3(3a+3b)
-9a-9b = -9a-9b
therefore LHS = RHS

Answer 2

Heya,

-9(a+b) = -3{(2a+b)+(a+2b)}

let us solve RHS,

=> -3{(2a+b)+(a+2b)}
= -3{ 2a + b + a + 2b}
= -3{3a + 3b}
= -3*3(a + b)
= -9(a + b)
= RHS

Hope this helps you...:)
Have a nice day ahead..