1. S= (c+a-b)(c+b-a)
<=> p(p-a)(p-b)(p-c)=4(p-b)(p-a)
<=> p(p-c)=16(p-b)(p-a)
<=> (a+b+c)(a+b-c)=16(a+c-b)(b+c-a)
<=> c^2-a^2-b^2=-30/17.ab
Từ gt => 1/2ab.sinC=c^2-(a-b)^2
=>sinC=...
Mà cosC=(a^2+b^2-c^2)/2ab
=> tan C=sinC/cosC=8/15
<=> p(p-a)(p-b)(p-c)=4(p-b)(p-a)
<=> p(p-c)=16(p-b)(p-a)
<=> (a+b+c)(a+b-c)=16(a+c-b)(b+c-a)
<=> c^2-a^2-b^2=-30/17.ab
Từ gt => 1/2ab.sinC=c^2-(a-b)^2
=>sinC=...
Mà cosC=(a^2+b^2-c^2)/2ab
=> tan C=sinC/cosC=8/15