a) 99 - 97 + 95 - 93 + 91 - 89 + ... + 7 - 5 + 3 - 1

=(99-97) + (95-93) + ... + (7-5) + (3-1)

=2 . 25

=50

b) 991 - 981 + 971 - 961 + ... + 31 - 21 + 11 - 1

=(991-981) + (971 - 961) + ... + (31-21) + (11-1)

=10 . 50

=500

\(\frac{\left(x^{95}+x^{94}\right)+.....+\left(x+1\right)}{\left(x^{31}+x^{30}\right)+.....+\left(x+1\right)}=\frac{x^{94}\left(x+1\right)+......+\left(x+1\right)}{x^{30}\left(x+1\right)+.....+\left(x+1\right)}=\frac{x^{94}+x^{92}+....+x^2+1}{x^{30}+x^{28}+....+x^2+1}=\frac{\left(x^2+1\right)x^{92}+x^{88}\left(x^2+1\right).....+\left(x^2+1\right)}{\left(x^2+1\right)x^{28}+\left(x^2+1\right)x^{24}+....+\left(x^2+1\right)}=\frac{x^{92}+x^{88}+......+x^4+1}{x^{28}+x^{24}+.....+x^4+1}=\frac{x^{88}\left(x^4+1\right)+x^{80}\left(x^4+1\right)+....+\left(x^4+1\right)}{x^{24}\left(x^4+1\right)+x^{16}\left(x^4+1\right)+.....+\left(x^4+1\right)}=\frac{x^{88}+x^{80}+....+1}{x^{24}+x^{16}+...+1}\)

\(=\frac{x^{80}\left(x^8+1\right)+x^{64}\left(x^8+1\right)+.....+\left(x^8+1\right)}{x^{16}\left(x^8+1\right)+\left(x^8+1\right)}=\frac{x^{80}+x^{64}+.....+1}{x^{16}+1}=\frac{x^{64}\left(x^{16}+1\right)+.....+x^{16}+1}{x^{16}+1}=x^{64}+x^{32}+1\)

\(a,\left(-5\right)+11+\left(-15\right)+21+\left(-25\right)+31+...+\left(-95\right)+101\\ =\left[\left(-5\right)+11\right]+\left[\left(-15\right)+21\right]+\left[\left(-25\right)+31\right]+...+\left[\left(-95\right)+101\right]\\ =6+6+6+...+6\left(10\text{ số }6\right)\\ =6\cdot10\\ =60\)

\(b,3+\left(-12\right)+13+\left(-22\right)+23+\left(-32\right)+...+93+\left(-102\right)\\ =\left[3+\left(-12\right)\right]+\left[13+\left(-22\right)\right]+\left[23+\left(-32\right)\right]+...+\left[93+\left(-102\right)\right]\\ =\left(-9\right)+\left(-9\right)+\left(-9\right)+...+\left(-9\right)\left(10\text{ số }-9\right)\\ =\left(-9\right)\cdot10\\ =-90\)

\(a,\left(-5\right)+11+\left(-15\right)+21+\left(-25\right)+31+...+\left(-95\right)+101\)

\(=\left[\left(-5\right)+11\right]+\left[\left(-15\right)+21\right]+\left[\left(-25\right)+31\right]+...+\left[\left(-95\right)+101\right]\)

\(=6+6+6+...+6\) (10 số 6)

\(=6.10=60\)

\(\)

\(a)-5+11+(-15)+21+(-25)+31+.......+(-95)+101\)

\(=(-5+11)+(-15+21)+(-25+31)+.....+(-95+101)\)

\(=6+6+6+..........+6\)(10 số 6)

\(=6.10\)

\(=60\)

Vậy....

Câu b tương tự

Đúng rồi

❓k hiểu lắm

=> Bạn đã có đáp án (tui ko biết where is câu hỏi).

24+25+26+...+31

Có 8 số hạng

Tổng là: (31+24)x8:2=220

Đ/s:...

2+4+...+100

Có số số hạng là: (100-2):2+1= 50 số

Tổng là: (100+2)x50:2=2550

Đ/s:...

xin lỗi, tính nhanh