\(\dfrac{-1}{39}+\dfrac{-1}{52}=\dfrac{-7}{156}\)

\(\dfrac{-6}{9}+\dfrac{-12}{16}=\dfrac{-17}{12}\)

\(\dfrac{-2}{5}-\dfrac{-3}{11}=\dfrac{-7}{55}\)

\(\dfrac{-34}{37}.\dfrac{74}{-85}=\dfrac{4}{5}\)

\(\dfrac{-5}{9}:\dfrac{-7}{18}=\dfrac{10}{7}\)

Chúc bạn học tốt!!!

a) \(\left(-\dfrac{1}{39}\right)+\left(-\dfrac{1}{52}\right)=\dfrac{-4-3}{156}=-\dfrac{7}{156}\)

b) \(\left(-\dfrac{6}{9}\right)+\left(-\dfrac{12}{16}\right)=-\dfrac{6}{9}-\dfrac{12}{16}=-\dfrac{17}{12}\)

c) \(-\dfrac{2}{5}-\left(-\dfrac{3}{11}\right)=-\dfrac{2}{5}+\dfrac{3}{11}=-\dfrac{7}{55}\)

d) \(\left(-\dfrac{34}{37}\right)\cdot\left(-\dfrac{74}{85}\right)=2\cdot\dfrac{2}{5}=\dfrac{4}{5}\)

e) \(\left(-\dfrac{5}{9}\right):\left(-\dfrac{7}{18}\right)=\dfrac{5}{9}\cdot\dfrac{18}{7}=5\cdot\dfrac{2}{7}=\dfrac{10}{7}\)

Chọn D

THAM KHẢO:

v chọn B

chữ xấu thế

A

\(A=4\left[\left(sin^2a+cos^2a\right)^3-3sin^2a.cos^2a\left(sin^2a+cos^2a\right)\right]-6\left[\left(sin^2a+cos^2a\right)^2-2sin^2a.cos^2a\right]\)

\(=4\left(1-3sin^2a.cos^2a\right)-6\left(1-2sin^2a.cos^2a\right)\)

\(=4-12sin^2a.cos^2a-6+12sin^2a.cos^2a\)

\(=-2\)

37:

\(AB=\sqrt{\left(-2-1\right)^2+\left(4-2\right)^2}=\sqrt{13}\)

\(AC=\sqrt{\left(3-1\right)^2+\left(5-2\right)^2}=\sqrt{13}\)

\(BC=\sqrt{\left(3+2\right)^2+\left(5-4\right)^2}=\sqrt{26}\)

Vì AB^2+AC^2=BC^2 và AB=AC

nên ΔABC vuông cân tại A

=>S ABC=1/2*AB*AC=1/2*13=13/2

AH=13/2*2:căn 26=13/căn 26=1/2*căn 26

Chọn A

Đường tròn (C) tâm \(I\left(-2;-2\right)\) bán kính \(R=5\)

Gọi đường thẳng d qua A có dạng: \(a\left(x-6\right)+b\left(y-17\right)=0\)

\(\Leftrightarrow ax+by-6a-17b=0\) (\(a^2+b^2\ne0\))

d là tiếp tuyến của (C) khi và chỉ khi \(d\left(I;d\right)=R\)

\(\Leftrightarrow\dfrac{\left|-2a-2b-6a-17b\right|}{\sqrt{a^2+b^2}}=5\)

\(\Leftrightarrow\left|8a+19b\right|=5\sqrt{a^2+b^2}\)

\(\Leftrightarrow\left(8a+9b\right)^2=25\left(a^2+b^2\right)\)

\(\Leftrightarrow\left(3a+4b\right)\left(13a+84b\right)=0\)

Chọn \(\left(a;b\right)=\left(4;-3\right);\left(84;-13\right)\)

Có 2 tiếp tuyến: \(\left[{}\begin{matrix}4\left(x-6\right)-3\left(y-17\right)=0\\84\left(x-6\right)-13\left(y-17\right)=0\end{matrix}\right.\) \(\Leftrightarrow...\)