①15又2/3*(-14又1/3)=47/3×（-43/3）=-2021/9
② [2x^2-(x+y)(x-y)][(z-x)(x+z)+(y-z)(y+z)]
=（2x²-x²+y²)(z²-x²+y²-z²)
=(x²+y²)(y²-x²)
=y^4-x^4
③ （a-2b+3c）(a+2b-3c)
=[a-(2b-3c)][a+(2b-3c)]
=a²-(2b-3c)²
=a²-4b²+12bc-9c²
④60又1/3*59又2/3
=64/3*179/3
=11456/9
⑤已知（a+b）^2=7,(a-b)^2=4,求a^2+b^2和ab的值
(a+b)²=7
a²+2ab+b²=7 ①
(a-b)²=4
a²-2ab+b²=4 ②
把①-②得：
4ab=3
ab=3/4
把①+②得：
2(a²+b²)=11
a²+b²=11/2
⑥在实数范围内因式分解a^4-4a^2+4=(a²-2)²=(a-√2)²(a+√2)²