=4k? +4k+ 1-4k? -4k
= 1 & gt; 0
∴AB is not equal to AC.
When △ABC is an isosceles triangle, one side =BC=5.
∴ Substitution x=5
5? -5(2k+ 1)+k? +k=0
k? -9k+20=0
K=5 or k=4
( 1)k=5,x? - 1 1x+30=0
∴x=6, x=6, namely AB=5, AC=6.
∴△abc perimeter =5+5+6= 16
Area = 1/2×6×4= 12.
(2)k=4,x? -9x+20=0
x=5,x=4
∴△ABC perimeter =4+5+5= 14
Area =1/2× 4×√ 21= 2 √ 21.