Question

Tìm x :

a) 10 + 15 + 20 +...x 300 + x =67

b) \(\frac{1}{42}+\frac{1}{30}+\frac{1}{20}+\frac{1}{12}+\frac{1}{6}+\frac{1}{2}-\frac{1}{x+1}=\frac{59}{77}\)

Cố gắng giúp mik nha. Hơi khó nhưng được 2 ****

Answer 1

a, 10+15+20+....+295+x.300+x=67

10+15+20+...+295+x(300+1)=67

10+15+20+...+295+x.301=67

8845+x.301=67

67-8845=x.301

-8878=x.301

x=-29/149/301

b, 

\(\frac{1}{7.6}+\frac{1}{6.5}+\frac{1}{5.4}+\frac{1}{4.3}+\frac{1}{3.2}+\frac{1}{2.1}-\frac{1}{x+1}=\frac{59}{77}\)

\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}-\frac{1}{x+1}=\frac{59}{77}\)

\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}-\frac{1}{x+1}=\frac{59}{77}\)\(1-\frac{1}{7}-\frac{1}{x+1}=\frac{59}{77}\)

\(\frac{6}{7}-\frac{1}{x+1}=\frac{59}{77}\)

\(\frac{1}{x+1}=\frac{6}{7}-\frac{59}{77}\)

\(\frac{1}{x+1}=\frac{1}{11}\)

suy ra x+1=11

suy ra x=10