請教三角函數

請教三角函數題目三題 謝謝!!
(1)\(\Delta ABC\)中\(\displaystyle cscA=\frac{cosA+cosB}{sinA+sinB}\),則\(\Delta ABC\)的形狀為？
(2)\(\Delta ABC\)中\(a^4+b^4+c^4+a^2b^2=2c^2(a^2+b^2)\),則\(∠C=\)？
(3)\(\Delta ABC\)中\(b^2sin^2C-c^2cos^2B=2bc\cdot cosBcosC\),則\(\displaystyle \frac{a^2+3ab+b^2}{a^2-ab+b^2}=\)？
答案：(1)直角三角形 (2)\(60^{\circ}\)或\(120^{\circ}\)  (3)5