Datos :
<img src="https://tex.z-dn.net/?f=A%3D%5Cfrac%7Bbh%7D%7B2%7D%5C%5Ch%3Db%2B4%5C%5CA%3D%5Cfrac%7Bb%28b%2B4%29%7D%7B2%7D%5C%2C%5Ctextup%7B%20resolviendo%20esta%20cuadratica%20se%20tiene%7D%5C%5CA%3D%5Cfrac%7Bb%5E%7B2%7D%2B4b%7D%7B2%7D%3D%5C%5C2A%3Db%5E%7B2%7D%2B4b%5C%5Cb%5E%7B2%7D%2B4b-2A%3D0%5C%5Cb%5E%7B2%7D%2B4b-2%28160%29%3D0%5C%5Cb%5E%7B2%7D%2B4b-320%3D0" />
Luego
<img src="https://tex.z-dn.net/?f=x%3D%5Cfrac%7B-b%5Cpm%5Csqrt%7Bb%5E%7B2%7D-4ac%7D%7D%7B2a%7D%3D%5Cfrac%7B-4%5Cpm%5Csqrt%7B4%5E%7B2%7D-4%281%29%28-320%29%7D%7D%7B2%281%29%7D%3D%5C%5Cx%3D%5Cfrac%7B-4%5Cpm%5Csqrt%7B16%2B1280%7D%7D%7B2%7D%5C%5Cx%3D%5Cfrac%7B-4%5Cpm%5Csqrt%7B1296%7D%7D%7B2%7D%5C%5Cx%3D%5Cfrac%7B-4%5Cpm36%7D%7B2%7D%5C%5Cx_%7B1%7D%3D%5Cfrac%7B-4%2B36%7D%7B2%7D%3D16%5C%5Cx_%7B2%7D%3D%5Cfrac%7B-4-36%7D%7B2%7D%3D-20" />
Descartando la raíz negativa se tiene :
<img src="https://tex.z-dn.net/?f=A%3D%5Cfrac%7Bbh%7D%7B2%7D%3D%5Cfrac%7Bb%28b%2B4%29%7D%7B2%7D%5C%5Cb%3D16%5C%5Ch%3D16%2B4%3D20" />
Comprobando :
<img src="https://tex.z-dn.net/?f=A%3D%5Cfrac%7Bbh%7D%7B2%7D%5C%5CA%3D%5Cfrac%7B%2816%29%2820%29%7D%7B2%7D%5C%5C160%3D160" />
Saludos.