# Finding Area

Updated February 11, 2017 | Infoplease Staff

### Square

A = a^{2}, in which *a* is one of the sides.

### Rectangle

A = ab, in which *a* is the base and *b* is the length.

### Parallelogram

A = bh, in which *b* is the base and *h* is the height.

### Circle

A = ?r^{2}, in which ? is 3.1416 and *r* is the radius.

### Ellipse

A = ?r_{1}r_{2}, in which ? is 3.1416, *r _{1}* is the longer radius, and

*r*is the shorter radius.

_{2}### Trapezoid

A = (h[b_{1} + b_{2}])/2, in which *h* is the height, *b _{1}* is the longer parallel side, and

*b*is the shorter parallel side.

_{2}### Triangle

**Given base and height:** A = (1/2)bh, in which b is the base and h is the height.

**Given side, angle, side (SAS):** (1/2) ab x sin?, in which *a* is one side, *b* is another side, and ? is the known angle.

**Given three sides:** when s = (a + b + c)/2 *(Heron's formula)*, in which *a, b,* and *c* represent the three sides.

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**See also:**