9x²-16（a+b)²
=[3x-4(a+b)][3x+4(a+b)]
=(3x-4a-4b)(3x+4a+4b)
1/2x⁴y²-1/8x²y⁴
=1/8x²y²(4x²-y²)
=1/8x²y²(2x-y)(2x+y)
9.8x10.2
=(10-0.2)(10+0.2)
=10²-0.2²
=100-0.04
=99.96