(7a-8b)(a-2b)+(a-8b)(a-2b)

=[6a+(a-8b)](a-2b)+(a-8b)(a-2b)
=6a(a-2b)+(a-8b)(a-2b)+(a-8b)(a-2b)
=6a(a-2b)+2(a-8b)(a-2b)
=[6a+2(a-8b)](a-2b)
=(6a+2a-16b)(a-2b)
=(8a-16b)(a-2b)
=8乘以(a-2b)的平方
=8（a平方-4ab+4b的平方）
=8a平方-32ab+32b的平方