true or false 1, If Ox and Oy are opposite rays then \(\widehat{xOy=180^o}\)2,If Ox and Oy are parallel then \(\widehat{xOy}=180^o\) or \(\widehat{xOy}=0^o\)3, If \(\widehat{xOy}=90^o\) then \(\widehat{xOy}\) is a straight angle4, If \(\widehat{xOy}\) +\(\widehat{yOz}=180^o\) then \(\widehat{xOy}\) and \(\widehat{yOz}\) are complementary5, If \(\widehat{xOy}\) is larger than \(\widehat{xOz}\) then \(\widehat{xOz}\) is an acute angle6, the lagest angle which is form by two rays is an obtuse...
Đọc tiếp
true or false
1, If Ox and Oy are opposite rays then \(\widehat{xOy=180^o}\)
2,If Ox and Oy are parallel then \(\widehat{xOy}=180^o\) or \(\widehat{xOy}=0^o\)
3, If \(\widehat{xOy}=90^o\) then \(\widehat{xOy}\) is a straight angle
4, If \(\widehat{xOy}\) +\(\widehat{yOz}=180^o\) then \(\widehat{xOy}\) and \(\widehat{yOz}\) are complementary
5, If \(\widehat{xOy}\) is larger than \(\widehat{xOz}\) then \(\widehat{xOz}\) is an acute angle
6, the lagest angle which is form by two rays is an obtuse angle
7, Two acute angles cannot be supplementary
8,\(\widehat{xOy}\) and \(\widehat{yOz}\) are adjacent
9, if \(\widehat{xOy}\) and \(\widehat{zOy}\)are supplementary then one of them must be an obtuse angle
10,if \(\widehat{xOy}\) and \(\widehat{yOz}\) are adjacent then \(\widehat{xOy}\) > \(\widehat{xOz}\)
11, If Ox lies between Oy and Oz then \(\widehat{xOy}\) and \(\widehat{yOz}\) are adjacent
Lời giải:
Đặt $a-\frac{b}{2}=x; \frac{a}{2}-b=y$ thì $45^0< x< 180^0; -45^0< y< 90^0$
$\cos x=\frac{-1}{4}; 45^0< x< 180^0$ nên $\sin x=\frac{\sqrt{15}}{4}$
$\sin y=\frac{1}{3}; -45^0< y< 90^0$ nên $\cos y=\frac{2\sqrt{2}}{3}$
\(P=72\cos (2x-2y)+49=72[2\cos ^2(x-y)-1]+49=144\cos ^2(x-y)-23\)
\(=144(\cos x\cos y+\sin x\sin y)^2-23=-4\sqrt{30}\)
Đáp án C.