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3-cos-x-4-cos-y-3-sin-x-4sin-y-5-find-x-amp-y-with-acute-angle-




Question Number 93256 by i jagooll last updated on 12/May/20
 { ((3 cos x = 4 cos y)),((3 sin x + 4sin y = 5)) :}  find x &y with acute angle
$$\begin{cases}{\mathrm{3}\:\mathrm{cos}\:\mathrm{x}\:=\:\mathrm{4}\:\mathrm{cos}\:\mathrm{y}}\\{\mathrm{3}\:\mathrm{sin}\:\mathrm{x}\:+\:\mathrm{4sin}\:\mathrm{y}\:=\:\mathrm{5}}\end{cases} \\ $$$$\mathrm{find}\:\mathrm{x}\:\&\mathrm{y}\:\mathrm{with}\:\mathrm{acute}\:\mathrm{angle}\: \\ $$
Commented by john santu last updated on 12/May/20
 { ((9 cos^2 x = 16 cos^2 y)),((9sin^2 x = 25−40sin y + 16sin^2 y)) :}  add (1) and (2)   9 = 41 − 40 sin y   sin y = (4/5) ⇒ y ≈53.13^o   ⇒3sin x+4sin y=5  3 sin x = 5−((16)/5) = (9/5)   sin x = (3/5) ⇒x = sin^(−1) ((3/5))  x ≈ 36.86^o
$$\begin{cases}{\mathrm{9}\:\mathrm{cos}\:^{\mathrm{2}} \mathrm{x}\:=\:\mathrm{16}\:\mathrm{cos}\:^{\mathrm{2}} \mathrm{y}}\\{\mathrm{9sin}\:^{\mathrm{2}} \mathrm{x}\:=\:\mathrm{25}−\mathrm{40sin}\:\mathrm{y}\:+\:\mathrm{16sin}\:^{\mathrm{2}} \mathrm{y}}\end{cases} \\ $$$$\mathrm{add}\:\left(\mathrm{1}\right)\:\mathrm{and}\:\left(\mathrm{2}\right)\: \\ $$$$\mathrm{9}\:=\:\mathrm{41}\:−\:\mathrm{40}\:\mathrm{sin}\:\mathrm{y}\: \\ $$$$\mathrm{sin}\:\mathrm{y}\:=\:\frac{\mathrm{4}}{\mathrm{5}}\:\Rightarrow\:\mathrm{y}\:\approx\mathrm{53}.\mathrm{13}^{\mathrm{o}} \\ $$$$\Rightarrow\mathrm{3sin}\:\mathrm{x}+\mathrm{4sin}\:\mathrm{y}=\mathrm{5} \\ $$$$\mathrm{3}\:\mathrm{sin}\:\mathrm{x}\:=\:\mathrm{5}−\frac{\mathrm{16}}{\mathrm{5}}\:=\:\frac{\mathrm{9}}{\mathrm{5}}\: \\ $$$$\mathrm{sin}\:\mathrm{x}\:=\:\frac{\mathrm{3}}{\mathrm{5}}\:\Rightarrow\mathrm{x}\:=\:\mathrm{sin}^{−\mathrm{1}} \left(\frac{\mathrm{3}}{\mathrm{5}}\right) \\ $$$$\mathrm{x}\:\approx\:\mathrm{36}.\mathrm{86}^{\mathrm{o}} \\ $$
Commented by i jagooll last updated on 12/May/20
thank you sir. cooll man ������

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