1.(3a+7b-8)(3a+7b+8)
=[(3a+7b)-8][(3a+7b)+8]
=(3a+7b)^2-8^2
=9a^2+42ab+49b^2-64
2.{(4x^3- 1/2y)^2+ 4y(2x^2- y/16)}÷(-2x)^2
=(16x^6-4x^3y+1/4y^2+8x^2y-1/4y^2)÷(-2x)^2
=(16x^6-4x^3y+8x^2y)÷(-2x)^2
=16x^6÷(-2x)^2-4x^3y÷(-2x)^2+8x^2y÷(-2x)^2
=4x^4-xy+2y