Two practical problems in seventh grade mathematics (about the complete square formula) 1. Given x + y = 4, (1) find the value of a ^ 2 + 1 / A ^ 2. (2) find the value of (A-2) (1 / A + 2) 2. Given x + y = 4, x ^ 2 + y ^ 2 = 14, find the value of XY 1. Given A-1 / a = 4, (1) find the value of a ^ 2 + 1 / A ^ 2. (2) find the value of (A-2) (1 / A + 2)

Where did a come from? Where did XY go?
Question 2: (x + y) ^ 2 = 16
Namely: x ^ 2 + y ^ 2 + 2XY = 16
Then: x ^ 2 + y ^ 2 + 2XY - (x ^ 2 + y ^ 2) = 16-14
2xy=2
xy=1

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