解:(1)原式=3xy2(﹣8x3y3)=﹣24x4y5; (2)原式=[c+(3a﹣2b)][c﹣(3a﹣2b)], =c2﹣(3a﹣2b)2, =c2﹣4b2+12ab﹣9a2; (3)原式=﹣2×299×0.599﹣(﹣1), =﹣2×(2×0.5)99+1, =﹣2×1+1, =﹣1; (4)原式=[(x+y)(x﹣y)](x2+y2)(x4+y4), =(x2﹣y2)(x2+y2)(x4+y4), =(x4﹣y4)(x4+y4), =x8﹣y8, 当x=()﹣1=2,y=﹣2时,原式=28﹣(﹣2)8=0; (5)∵AB∥CD, ∴∠BEF=180°﹣EFD,∠CFG=∠GMA=52°, ∴∠GFD=180°﹣∠CFG=128° 又∵EF平分∠GFD, ∴∠EFD=∠GFD=64°, ∴∠BEF=180°﹣∠EFD=116°. |