Algebra and Trigonometry 10th Edition

$E=\sqrt {12.5} \sin \theta+\sqrt {12.5} \cos \theta$
We have: $\tan \dfrac{\pi}{4}=1$ When $a=b$; $\sqrt {a^2+b^2} = 5$ $\implies 5=\sqrt {2a^2}$ or, $a=b=\sqrt {12.5}$ Now, $E=\sqrt {12.5} \sin \theta+\sqrt {12.5} \cos \theta$