Question

不解方程组2X+Y=6,X-3Y=1.求7Y(X-3Y)^2-2(3Y-X)^3的值

Answer 1

7Y(X-3Y)^2-2(3Y-X)^3=(X-3Y)^2(7Y-6Y+2X)
=(X-3Y)^2(2X+Y)=6

Answer 2

(X-3Y)^2-2(3Y-X)^3
=7Y(3Y-X)^2-2(3Y-X)^3
=(3Y-X)^2[7Y-2(3Y-X)]
=(3Y-X)^2(7Y-6y+2X)
=(3Y-X)^2(2X+Y)
=6(-1)^2
=6