Question

1. Tìm x
a) 1/15 + 1/35 + 1/63 + 1/99 + ... + 1/ x. (x+2) = 16/99
b) x/2 = 3/5
c ) x/ -4 = -4/x
d) GTTĐ của x+2 = 1/2 - 1/3
Các bạn giúp mình nhé!Chiều nay mình phải nộp rùi ^^
Ai đúng và nhanh nhất mình sẽ tick cho nè <3
Thank you :3

Answer 1

a) \(\dfrac{1}{15}+\dfrac{1}{35}+\dfrac{1}{63}+\dfrac{1}{99}+...+\dfrac{1}{x.\left(x+2\right)}=\dfrac{16}{99}\)

\(\dfrac{1}{3.5}+\dfrac{1}{5.7}+\dfrac{1}{7.9}+\dfrac{1}{9.11}+...+\dfrac{1}{x.\left(x+2\right)}=\dfrac{16}{99}\)

\(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{x}-\dfrac{1}{\left(x+2\right)}=\dfrac{16}{99}.2\)

\(\dfrac{1}{3}-\dfrac{1}{\left(x+2\right)}=\dfrac{32}{99}\)

\(\dfrac{1}{\left(x+2\right)}=\dfrac{1}{3}-\dfrac{32}{99}\)

\(\dfrac{1}{\left(x+2\right)}=\dfrac{1}{99}\)

\(\Rightarrow x+2=99\\ x=99-2\\ x=97\)