(101 - 1) :2 + 1= 51

(101+1) x51:2=2601

\(101^2=\left(100+1\right)^2=10000+200+1=10201\\ 9999^2=\left(10000-1\right)^2=100000000-20000+1=99980001\\ 47\cdot53=\left(50-3\right)\left(50+3\right)=2500-9=2491\\ 991\cdot1009=\left(1000-9\right)\left(1000+9\right)=1000000-81=999919\)

a: \(101^2=10201\)

b: \(9999^2=99980001\)

c: \(47\cdot53=2491\)

d: \(991\cdot1009=999919\)

Số các số hạng trong tổng trên là: (215 - 1) : 2 + 1 = 108 (số hạng)

Tổng trên bằng: (1 + 215) x (108 : 2) = 216 x 54 = 11664

thanh you

a: \(\left(-34\right)\cdot11\)

\(=-34\left(10+1\right)\)

\(=-34\cdot10-34\cdot1=-340-34=-374\)

b: \(250\cdot\left(-21\right)\)

\(=-250\left(20+1\right)\)

\(=-250\cdot20-250\cdot1=-5000-250=-5250\)

c: \(\left(-23\right)\cdot101\)

\(=\left(-23\right)\left(100+1\right)\)

\(=-23\cdot100-23\cdot1=-2300-23=-2323\)

d: \(31\cdot\left(-99\right)=-31\cdot99\)

\(=-31\left(100-1\right)\)

\(=-31\cdot100+31\cdot1\)

=-3100+31

=-3069

a)=-374                   b)=-5250

c)=-2323                  d)=-3069

Đáp án B

a: \(101^2+128\cdot26-27^2\)

\(=\left(101-27\right)\left(101+27\right)+128\cdot26\)

\(=74\cdot128+128\cdot26=128\cdot\left(74+26\right)=128\cdot100=12800\)

\(531^2-659\cdot403-128^2\)

\(=\left(531-128\right)\left(531+128\right)-659\cdot403\)

\(=403\cdot659-659\cdot403=0\)

b: \(\left(4n+3\right)^2-25\)

=(4n+3-5)(4n+3+5)

=(4n-2)(4n+8)

\(=2\left(2n-1\right)\cdot4\cdot\left(n+2\right)=8\left(2n-1\right)\left(n+2\right)\) ⋮8

sửa đề câu a  và câu b  nhá  , mik nghĩ đề như này :

  \(\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{213\cdot215}\)

 \(=\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{213}-\frac{1}{215}\)

= \(\frac{1}{1}-\frac{1}{215}\)

\(=\frac{214}{215}\)

b, đặt \(A=\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+\frac{1}{5\cdot7}+\frac{1}{7\cdot9}+...+\frac{1}{213\cdot215}\)

    \(A\cdot2=\frac{2}{1\cdot3}+\frac{2}{3.5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{213\cdot215}\)

\(A\cdot2=\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{213}-\frac{1}{215}\)

\(A\cdot2=\frac{1}{1}-\frac{1}{215}\)

\(A\cdot2=\frac{214}{215}\)

\(A=\frac{214}{215}:2\)

\(A=\frac{107}{215}\)

@ミ★Ŧɦươйǥ★彡 cảm ơn bạn nhiều

Kết quả phép tính là đáp án C.  2 13 .