Perimeter:
The perimeter of the triangle is the sum of its sides.
We have then:
P = 8 + 12 + 10
P = 30 units
Semi-perimeter:
In geometry, the semiperimeter of a polygon is half its perimeter.
s = P / 2
s = 30/2
s = 15 units.
Area:
Knowing the semiperimeter and the sides, the area is:
A = root (s * (s-a) * (s-b) * (s-c))
where,
s: semi-meter
a, b, c are sides.
A = root (15 * (15-8) * (15-12) * (15-10))
A = 39.68626967
A = 40 units ^ 2