3 cây mía nặng số kg là:

3 x 35=105 (kg)

Choose the letter A, B, C or D to answer these following questions

This is Alex. He is twenty years old. He is a weight-lifter. He is tall and strong. He spends 2 hours practicing weight-lifting every day. Weightlifting is a hard and dangerous sports to play. Sometimes, Alex hurts himself while doing the sport. But he never gives up. He wants to be a champion in the future. All the family members are proud of him. He will take part in a sport competition next week. Would you want to come along and watch the match?

Question: When will he take part in a sport competition?

A. next week

B. next month

C. next year

D. next day

chieu rong la sao 

a, \(\dfrac{1}{4}x^2+3x+9=\dfrac{1}{4}x.x+3x+9=\left(\dfrac{13}{4}x+3\right)^2\)

Vì \(\left(\dfrac{13}{4}x+3\right)^2\ge0\) nên \(\left(\dfrac{13}{4}x+3\right)^2\)luôn dương với mọi x \(\Rightarrow\dfrac{1}{4}x^2+3x+9\) không âm , bài b,c làm tương tự thoy