Answer:
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
