Ta có c=45oc=45o

Ta có tana=13;tanb=12tan⁡a=13;tan⁡b=12

Ta có tan(a+b)=tana+tanb1−tana.tanb=13+121−13.12=1⇒a+b=45otan⁡(a+b)=tan⁡a+tan⁡b1−tan⁡a.tan⁡b=13+121−13.12=1⇒a+b=45o

⇒a+b+c=45o+45o=90o