Question

1. Tính bằng cách thuận tiện nhất

(1 + 3 + 5 + ...+ 2005) x (125125 x 127 - 127127 x 125)

2. Tìm x biết :

(7 x 13 + 8 x 13) : ( 29/3 - x) = 39

Answer 1

1. (1 + 3 + 5 + ... + 2005) . ( 125125.127 - 127127.125)

Ta có 125125.127 - 127127.125

=125.1001.127 - 127.1001.125

=0

=> (1 + 3 + 5 + ... + 2005) . ( 125125.127 - 127127.125)

= (1 +3 + 5 +...+ 2005) . 0

=0

Answer 2

Bài 1:

\(\left(1+3+5+...+2005\right)\cdot\left(125125.127-127127.125\right).\)

\(=\left(1+3+5+...+2005\right)\left(125.1001.127-127127.125\right).\)

\(=\left(1+3+5+...+2005\right)\left(125.127127-127127.125\right).\)

\(=\left(1+3+5+...+2005\right).0=0.\)

Vậy.....

Bài 2:

\(\left(7.13+8.13\right):\left(\dfrac{29}{3}-x\right)=39.\)

\(\left[\left(7+8\right)13\right]:\left(\dfrac{29}{3}-x\right)=39.\)

\(\left[15.13\right]:\left(\dfrac{29}{3}-x\right)=39.\)

\(195:\left(\dfrac{29}{3}-x\right)=39.\)

\(\dfrac{29}{3}-x=195:39.\)

\(\dfrac{29}{3}-x=5.\)

\(\Rightarrow x=\dfrac{29}{3}-5.\)

\(\Rightarrow x=\dfrac{29}{3}-\dfrac{15}{3}=\dfrac{14}{3}.\)

Vậy.....

~ Hok tốt!!! ~