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The perimeter is AB + BC + AC.

 

BC  =  AK + KB  =  6 + 8  =  14

 

Since AK is an altitude, triangle(ABK) is a right triangle. 

Its bases are AK = 6 and KB = 8.

To find AB, use the Pythagoren Theorem:  AB²  =  AK² + KB²  =  6² + 8²

Complete this equation to find the value of AB.

 

Also, triangle(AKC) is a right triangle.

Its bases are KC = 6 and AK = 6.

To find AC:  AC²  =  KC² + AK²  =  6² + 6²

Complete this equation to find the value of AC.

 

Now, use:  AB + BC + AC to find the perimeter.