0,75g =))???

750

a. Ta có:

 \(\left\{{}\begin{matrix}\widehat{A}=\widehat{B}\\\widehat{B}=2\widehat{C}\end{matrix}\right.\)

 \(\Rightarrow\widehat{A}+\widehat{B}=4\widehat{C}\)  

Xét tam giác ABC có:

\(\widehat{A}+\widehat{B}+\widehat{C}=180^o\) (định lí tổng 3 góc trong 1 tam giác)

Mà \(\widehat{A}+\widehat{B}=4\widehat{C}\)

\(\Rightarrow4\widehat{C}+\widehat{C}=180^o\)

\(5\widehat{C}=180^o\)

\(\widehat{C}=180^o:5\)

\(\widehat{C}=36^o\)

\(\Rightarrow\left\{{}\begin{matrix}\widehat{B}=2\widehat{C}=2.36^o=72^o\\\widehat{A}=\widehat{B}=72^o\end{matrix}\right.\)

b. Ta có: \(\widehat{A}=\widehat{B}\)

\(\Rightarrow\) Tam giác ABC cân tại \(C\)

99

a. A = -(45 - x) - (-24 - x) + (-55 - x)

       = -45 + x + 24 + x - 55 - x

       = (x + x - x) + (-45 + 24 - 55)

       = x - 76

b. B = x - 42 - [(13 + x) - (17 - x)]

        = x - 42 - (13 + x - 17 + x)

        = x - 42 - 13 - x + 17 - x

        = (x - x - x) + (-42 - 13 + 17)

        = -x - 38

c.  C = -(20 - x) - [17 + (-x)]

        = -20 + x - (17 - x)

        = -20 + x - 17 + x

        = (x + x) + (-20 - 17)

        = 2x - 37

Which