Question

determine cos x sendo sen x = -5/13

Answer 1

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$\large\boxed{\begin{array}{l}\sf vou~admitir~que~x\in 4^{o}~quadrante\\\sf sen\,x=-\dfrac{5}{13}\implies sen^2\,x=\dfrac{25}{169}\\\\\sf cos^2\,x=\dfrac{169}{169}-\dfrac{25}{169}\\\\\sf cos^2\,x=\dfrac{144}{169}\\\\\sf cos\,x=\sqrt{\dfrac{144}{169}}\\\\\sf cos\,x=\dfrac{12}{13}\end{array}}$