肯定对哦
[(x+2y)(x-2y)-(2x-y)^2+(3x-y)(2x-5y)]/(-1/2x)
=[(x^2-4y^2)-(4x^2-4xy+y^2)+(6x^2-17xy+5y^2)]/(-1/2x)
=(x^2-4y^2-4x^2-y^2+6x^2-17xy+5y^2)/(-1/2x)
=(3x^2-13xy)/(-1/2x)
=-6x+26y
79*3.14+10*1.34+11*1.34
=79*3.14+1.34*(10+11)
=79*3.14+1.34*21
=(100-21)*3.14+1.34*21
=314-21*3.14+1.34*21
=314-21*(3.14-1.34)
=314-21*1.8
=314-(20+1)*1.8
=314-36-1.8
=276.2