La toate subpunctele se foloseşte formula: (x-y)(x+y) = x²-y²
a) (x+3)(x-3) = x²-9
b) (a-2)(a+2) = a²-4
c) (b-4)(b+4) = b²-16
d) (2a+5b)(2a-5b) = 4a²-25b²
e) (6a+5)(6a-5) = 36a²-25
f) (5x-1)(5x+1) = 25x²-1
g) (8x+5)(8x-5) = 64x²-25
h) (7x-3)(7x+3) = 49x²-9
i) (2x-3y)(2x+3y) = 4x²-9y²
j) (4x+9)(4x-9) = 16x²-81
k) (5x+6)(5x-6) = 25x²-36
l) (3x+8)(3x-8) = 9x²-64
