6x×(3xy)
=6×3×x×x×y
=18x²y
(-7x)×4/7xy²
=-7×4/7×x×x×y²
=-4x²y²
(-3ab)(2a²b+ab-1
=-3ab×2a²b-3ab×ab+3ab×1
=-6a³b²-3a²b²+3ab
(2×10³)(3×10^5)(1/2×10²)
=2×3×1/2×10³×10^5×10²
=3×10^10
(2a+3b)(3a-2b)
=2a×3a-2a×2b+3b×3a-3b×2b
=6a²-4ab+9ab-6b²
=6a²+5ab-6b²
3x²-(x+3)(x-4)
=3x²-(x²-4x+3x-12)
=3x²-x²+4x-3x+12
=2x²+x+12
(2x+y)(2x-y)
=(2x)²-y²
=4x²-y²
(x-2y)(2y+x)
=(x-2y)(x+2y)
=x²-(2y)²
=x²-4y²
(-1/2a-2b)(1/2a-b)
=-1/2a×1/2a+1/2a×b-2b×1/2a+2b×b
=-1/4a²+1/2ab-ab+2b²
=-1/4a²-1/2ab+2b²
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