Answer:
It's the law of cosines
Step-by-step explanation:
law of cosines states that [tex]c^{2} =a^{2} +b^{2} -2ab (cos(\alpha ))[/tex]
so we know that a = 7, b = 4, and alpha would be 135 degrees, so just plugging it in gets us 49+16-2*7*4*(-0.707) = 65 + 39.59 = 104.59
