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Let x be an acute angle such that \tan x + \sec x = 0. Find cosx.

 Feb 11, 2024

Best Answer 

 #1
avatar+410 
+2

What do we know about tan(x) and sec(x)? We know tan(x)=sin(x)cos(x),sec(x)=1cos(x). Now use these, and replace them in the equation. 

We get sin(x)cos(x)+1cos(x)=0. Multiplying by cos(x), with the restriction, cos(x) is not equal to 0, gives us sin(x)+1=0, or sin(x)=1. So, now we use the formula, sin2(x)+cos2(x)=1, we get cos2(x)=0,cos(x)=0. Notice there is only one solution, because +/- 0 is always 0.

But we see from ealier that cos(x) is not 0, so we have no solution.

 Feb 11, 2024
 #1
avatar+410 
+2
Best Answer

What do we know about tan(x) and sec(x)? We know tan(x)=sin(x)cos(x),sec(x)=1cos(x). Now use these, and replace them in the equation. 

We get sin(x)cos(x)+1cos(x)=0. Multiplying by cos(x), with the restriction, cos(x) is not equal to 0, gives us sin(x)+1=0, or sin(x)=1. So, now we use the formula, sin2(x)+cos2(x)=1, we get cos2(x)=0,cos(x)=0. Notice there is only one solution, because +/- 0 is always 0.

But we see from ealier that cos(x) is not 0, so we have no solution.

hairyberry Feb 11, 2024

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