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1/ đúng
2/ đúng
3/sai thiếu điều kiện M,A,B thẳng hàng
a sai vì tia Ox phải sửa thành Oz thì 2 góc xOy và yOz kề nhau
b sai vì Oy phải nằm giữa 2 tia Ox và Oz thì 2 góc xOy và yOz mới kề nhau
O y x a b
a) Ta có: \(\widehat{xOa}=\widehat{xOy}-\widehat{aOy}=135-90=45\) độ
b) Ta có: \(\widehat{xOb}+\widehat{xOa}=180\)(kề bù)
\(\Rightarrow\widehat{xOb}+45=180\Rightarrow\widehat{xOb}=180-45=135\)độ
Tính \(\widehat{yOb}\)có thể không cần giải cũng biết nhưng thôi mình giải ra đàng hoàng cho bạn nha.
Ta có: \(\widehat{yOb}+\widehat{aOy}=180\)(kề bù)
\(\Rightarrow\widehat{yOb}+90=180\Rightarrow\widehat{yOb}=180-90=90\)độ
\(135>90\)
Vậy: \(\widehat{xOb}>\widehat{yOb}\)
a,ta có gAOC + gCOD + gDOB = gAOB = 120 độ
mà gAOC=30 độ ; gDOB=35 độ =>gCOD = 120-30-35 = 55 độ
ta có gCOD + gDOB = gCOB
mà gCOD = 55 độ ; gDOB = 35 độ
=> gCOB = 55+35 = 90 độ
Theo mjk là sai
viết có dấu cái