=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.