=32.(10-25)-35.18+32.35

=32.(10-25+35)-35.18

=32.20-630

=640-630

=10

\(32\left(10-25\right)-35\left(18-32\right)\)

\(=32\left(10-25\right)-35\times18+35\times32\)

\(=32\left(10-25+35\right)-35\times18\)

\(=32\times20-35\times18\)

\(=640-630\)

\(=10\)

B = -34x + 34y

B = -34.(x - y)

B = -34.2 = -68

Vậy B = -68

C = ax - ay + bx - by 

C = a(x - y) + b(x - y)

C = (a + b).(x - y)

C = (-7).1 = -7

Vậy C = -7

Chúc em học tốt!!!

\(B=-34x+34y\)

\(\Leftrightarrow B=-34\left(x-y\right)\)

\(\Leftrightarrow B=-34\times2\)

\(\Leftrightarrow B=-68\)

\(C=ax-ay+bx-by\)

\(\Leftrightarrow C=a\left(x-y\right)+b\left(x-y\right)\)

\(\Leftrightarrow C=\left(a+b\right)\left(x+y\right)\)

\(\Leftrightarrow C=-7\times1\)

\(\Leftrightarrow C=-7\)

-2.(x+3)-15=3.(4+2x)+7

-2x - 6 - 16 = 12 + 6x + 7 

-2x - 6x = 12 + 7 + 6 + 16 

 -8x       = 41

     x      = -5,125

\(-2.\left(x+3\right)-15=3.\left(4+2x\right)+7\)

\(-2x-6-15=12+6x+7\)

\(-2x-6x=12+7+6+15\)

\(-8x=40\Leftrightarrow x=-5\)

Vậy...

Chúc em học tốt!!!

Đặt  A = 5.6 + 6.7 + 7.8 + 8.9 +...+ 97.98

 => 3A = 5.6.3 + 6.7.3 + 7.8.3 + 8.9.3 + ...+ 97.98.3

3A = 5.6.(7-4) + 6.7.(8-5) + 7.8(9-6) + 8.9.(10-7) +...+ 97.98.(99-96)

3A = 5.6.7 - 4.5.6 + 6.7.8 -5.6.7 + 7.8.9 - 6.7.8 + 8.9.10 - 7.8.9 + ...+ 97.98.99 - 96.97.98

3A = 97.98.99 - 4.5.6

A = 313 658

A = 1 + 7 + 7^2 + 7^3 + ...+ 7^39

=> 7A = 7 + 7^2 + 7^3 + 7^4 + ....+ 7^40

=> 7A - 7 = 7^40 - 1

\(A=\frac{7^{40}-1}{6}\)