Question

已知X-Y=5，(X+Y)方=49，求X方+Y方的值

Answer 1

X-Y=5，两边平方得X^2-2XY+Y^2=25 (1)(X+Y)方=49左边展开得X^2+2XY+Y^2=49 (2)(1)+(2)2X^2+2Y^2=74X^2+Y^2=37

Answer 2

X-Y=5(X-Y)方=25（X+Y)方=49两式相加得2（X方+Y方）=25+49=74X方+Y方=37

Answer 3

(X+Y)^2=49所以X+Y=7 又因为X-Y=5所以X=6 Y=1所以X^2+Y=36+1=37

Answer 4

37