數學方程式, 求解

2^(x+y)+2^(2x-y)=16 = 2^3 + 2^3

x + y = 3......(1)
2x - y = 3......(2)

(1)+(2) :

3x = 3+3

x = 2

y = 1

3^(x-y)/3^(y-x) +3^(2xy)=90

[3^(x-y)][3^(x-y)] + 9^(xy) = 90

9^(x-y) + 9^(xy) = 90

when x = 2 and y = 1 :

9^(2-1) + 9^(2*1) = 9 + 81 = 90

so x = 2 and y = 1 for both equations