Ta có :

\(M=a\left(a+2\right)-a\left(a-5\right)-7\)

\(M=a^2+2a-a^2+5a-7\)

\(M=7a-7\)

\(M=7\left(a-1\right)⋮7\)

=> đpcm

My cousin, Peter (have)…has……..a dog. It (be)…is……..an intelligent pet with a short tail and big black eyes. Its name (be)…is……..Kiki and it (like)……likes…..eating pork. However, it (never/ bite)……bits…..anyone; sometimes it (bark)……barks …..when strange guests visit. To be honest, it (be)…is……..very friendly. It (not/ like)……does not like…..eating fruits, but it (often/ play)…often plays……..with them. When the weather (become)…becomes……..bad, it (just/ sleep)……just sleep…..in his cage all day. Peter (play)……plays…..with Kiki every day after school. There (be)……are…..many people on the road, so Peter (not/ let)……does not let…..the dog run into the road. He (often/ take)……often takes.....Kiki to a large field to enjoy the peace there. Kiki (sometimes/ be)…sometimes is……..naughty, but Peter loves it very much.

Xét \(\Delta OMA\) và \(\Delta OMB\) có :

\(\widehat{O_1}=\widehat{O_2}\) ( OM là tia phân giác )

Chung OM

\(\widehat{A}=\widehat{B}=\left(=90^0\right)\)

=> \(\Delta OMA\)=\(\Delta OMB\) ( CH - GN )

=> OA = OB

Gọi giao điểm của AB và OM là H

Dễ dàng c/m \(\Delta AOH=\Delta BOH\) ( c_g_c )

=> \(\widehat{AHO}=\widehat{BHO}\)

Mà hai góc trên là hai góc kề bù

=> \(\widehat{AHO}=\widehat{BHO}=90^0\)

=> đpcm