given a right-angled triangle with perimeter 18. The sum of the squares of the three side lengths is 128. What is the area of the triangle ?

9units²

Step-by-step explanation:

A triangle has 3 sides. Let the length of the three sides be a, b, c.

If the perimeter of the triangle is 18, then;

P = a+b+c

a+b+c = 18... 1

If the sum of the squares of the three side lengths is 128, this means;

a²+b²+c² = 128... 2

Since the triangle is also right angled, according to Pythagoras theorem;

c² = a²+b²... 3 (taking c as the hypotenuse)

Substitute equation 3 into 2;

(a²+b²)+c² = 128

c²+c² = 128

2c² = 128

c² = 128/2

c² = 64

c = √64

c = 8

Substituting c = 8 into 1

a+b+c = 18

a+b+8=18

a+b = 10 3

Substituting c = 8 into 2

a²+b²+c² = 128

a²+b²+8² = 128

a²+b²+64 = 128

a²+b²= 64 4

Solve equation 3 and 4 simultaneously;

a+b = 10

a²+b²= 64

From 4; a = 10-b

Substitute a = 10-b into 4;

(10-b)²+b² = 64

100-20b+b²+b² = 64

2b²-20b+100-64 = 0

2b²-20b+36 = 0

Divide through by 2:

b²-10b+18 = 0

b = 10±√10²-4(18)/2

b = 10±√100-72/2

b =( 10±√28)/2

b =(10±√4×7)/2

b = (10±2√7)/2

b = 5±√7

Hence b = 5+√7

If a+ b = 10

a+(5+√7 ) = 10

a = 10-(5+√7)

a = 10-5-√7

a = 5-√7

Area of the triangle A = 1/2 ab

A = 1/2 × (5+√7) × (5-√7)

A = 1/2 × (25-5√7+5√7-7)

A = 1/2 × (25-7)

A = 1/2 × 18

A = 9

Hence the are of the triangle is 9units²

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