Cho tam giác ABC vuông ở B, kéo dài AC về phía C một đoạn CD=AB=1, góc CBD=30 độ. Tính AC.
Cho tam giác ABC vuông ở B, kéo dài AC về phía C một đoạn CD=AB=1, góc CBD=30 o . Tính AC. Giải: Lấy điểm E trên BD sao cho AB//CE ð ⃤ ABC ~ ⃤ CED ð ð CE.AD=CD.AB=1.1=1 Gọi x=AC Tac có: (pitago) Tam giác BCE vuông tại C (vì góc B bằng góc C so le) => Thay vào biểu thức trên(màu đỏ), ta được: =>(x 2 -1)(x+1) 2 =3 ó (x 2 -1)(x 2 +2x+1)=3 ó x 4 +2x 3 +x 2 -x 2 -2x-1=3 ó x 4 +2x 3 -2x-4=0 ó x 3 (x+2)-2(x+2)=0 ó (x+2)(x 3 -2)=0 ó x 3 -2=0 (x+2>0 vì x là số dương) =>
LOL Trump is still attacking the media for its coverage of his inauguration crowd (or lack thereof)
ReplyDelete"It's all a phony deal folks. But I saw a picture the other night of practically no people! It was taken hours before our great day."
Trump goads the crowd into booing "the fake news," then suggests he was just being sarcastic when he called for Russian hackers to go after Hillary Clinton's emails during a 2016 news conference.
ReplyDeleteThe crowd responds with "lock her up!" chants