A simple method to calculate the square of (half a-b) - quarter (a + b) (a-b)

A simple method to calculate the square of (half a-b) - quarter (a + b) (a-b)

=(a²/4-ab+b²)-(a²-b²)/4
=-ab+5b²/4

Using simple method to calculate 75 times 2.6 square - 12x3.5 square

75*2.6²-12*3.5²
=3*25*2.6²-3*4*3.5²
=3[(5*2.6)²-(2*3.5)²]
=3(13+7)(13-7)
three hundred and sixty

Let a = (0 10,2 0 - 1,3 41), I = (1 00,0 10,0 01), find the (I + a) - 1 power

(I+A,I) =
1 1 0 1 0 0
2 1 -1 0 1 0
3 4 2 0 0 1
r2-2r1,r3-3r1
1 1 0 1 0 0
0 -1 -1 -2 1 0
0 1 2 -3 0 1
r1+r2,r3+r2,r2*(-1)
1 0 -1 -1 1 0
0 1 1 2 -1 0
0 0 1 -5 1 1
r1+r3,r2-r3
1 0 0 -6 2 1
0 1 0 7 -2 -1
0 0 1 -5 1 1
(I+A)^-1 =
-6 2 1
7 -2 -1
-5 1 1