• anonymous
If A is acute and cos2A = -7/9 find without a calculator: a) cosA b) sinA
  • Stacey Warren - Expert
Hey! We 've verified this expert answer for you, click below to unlock the details :)
At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga. Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus. Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
  • katieb
I got my questions answered at in under 10 minutes. Go to now for free help!
  • anonymous
Use a) Cos2A= [2Cos^2(A)-1]=(-7/9) b) SinA=Sqrt(1-cos^2(A))
  • e.mccormick
Because A is acute, it is between 0 and 90 degrees. You can use the half angle formula, but in this case it is not really needed. You just need to see where cos2A = -7/9, then take half of that. Should be two possible answers and only one of them will be acute. Then develop your solutions from there.
  • anonymous
\[\cos 2A=2\cos ^{2}A-1=-\frac{ 7 }{9 }\] \[2\cos ^{2}A=\frac{ -7 }{ 9 }+1=\frac{ 2 }{ 9 }\] \[\cos ^{2}A=\frac{ 1 }{ 9 }\] \[\cos A=\frac{ 1 }{ 3 } ...\left( A is accute \right)\] Again \[\cos 2A=1-2\sin ^{2}A\] You can find sin A

Looking for something else?

Not the answer you are looking for? Search for more explanations.