先化简,再求值: a − b a ÷ ( a − 2 ab − b 2 a ) ,其中 a = 2 , b = 2 − 3 .
计算: (1)x2+5y-4x2-3y-1 (2)7a+3(a-3b)-(b-a)
计算: (1)-3-5+12; (2)(-81)÷×÷(-16); (3)-32-25×(-)2; (4)-24×(-+-); (5)-14-(1+0.5)×÷4; (6)-22×-(-1)2÷(-)-(-1)5.
计算 (1) (2) (3) (4) (5) (6)19×(-12)
计算题 (1); (2); (3); (4) ;
计算: (1); (2); (3); (4).