Question

若x-3y=4,x乘以y=2/5,求(x+3y)²的值

Answer 1

x*y
=
2/5
即0.4

x-3y
=
4
→(x-3y)^2
=
16
→
x^2
-
6xy
+
9y^2
=
16
→
x^2
+
9y^2
=
16
+
6*(0.4)
即
18.4
(x+3y)^2
=
x^2
+
6xy
+
9y^2
=
18.4
+
6*0.4
=20.8
即20又4/5
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