tự vẽ hình

a,

Ta có :

\(\widehat{xOt}+\widehat{tOy}=180^o\)

=> \(50^o+\widehat{tOy}=180^o\)

=> \(\widehat{tOy}=130^o\)

b,

Ta có :

\(\widehat{tOy}=130^o\) (cmt)

Mà \(\widehat{xOt'}\) là góc đối

=> \(\widehat{xOt'}=130^o\)

Ta có :

\(\widehat{xOt}+\widehat{xOt'}=\widehat{tOt'}\)

=> \(50^o+130^o=\widehat{tOt'}\)

=> \(\widehat{tOt'}=180^o\)

c,

Ta có :

\(\widehat{xOt}\) và \(\widehat{yOt'}\) là hai góc đối

Mà \(\widehat{xOt}=50^o\) (gt)

=> \(\widehat{yOt'}=50^o\)

d,

Ta có :

\(\widehat{xOt'}=130^o\) (cmt)

1,

A

2,

\(a,\left(\dfrac{6}{11}+\dfrac{5}{11}\right)\times\dfrac{3}{7}=1\times\dfrac{3}{7}=\dfrac{3}{7}\)

\(b,\dfrac{2}{7}:\dfrac{2}{3}-\dfrac{2}{7}=\dfrac{2}{7}\times\dfrac{3}{2}-\dfrac{2}{7}=\dfrac{3}{7}-\dfrac{2}{7}=\dfrac{1}{7}\)

1,

\(a,=-21x^3+28x^2y\)

\(b,=5x^2-4x-15x+12\)

= \(5x^2-19x+12\)

\(c,=4x^2-4x+1\)

\(d,=x^2-3x+3x-9=x^2-9\)

3,

Xét Δ ABC cân tại A, có :

\(\widehat{B}=\widehat{C}=50^o\)