Find the area of a rhombus if its vertices are (3, 0), (4, 5), (– 1, 4) and (– 2, – 1) taken in order. [Hint : Area of a rhombus = \(\frac{1}{2}\) (product of its diagonals)]

Let (3, 0), (4, 5), (−1, 4) and (−2, −1) are the vertices A, B, C, D of a rhombus ABCD.
Length of diagonal AC=\(\sqrt{[3-(-1)]^2+(0-4)}\)
= \(\sqrt{16+16}=4\sqrt2\)
Length of diagonal BD=\(\sqrt{[4-(-2)]^2+[5-(-1)]^2}\)
=\(\sqrt{36+36}=6\sqrt2\)
Therefore the area of rhombus ABCD = \(\frac{1}{2}\times4\sqrt2\times6\sqrt2\)
= 24 square units
Determine if the points (1, 5), (2, 3) and (– 2, – 11) are collinear
In a classroom, 4 friends are seated at points A, B, C and D. Champa and Chameli walk into the class and after observing for a few minutes Champa asks Chameli, “Don’t you think ABCD is a square?” Chameli disagrees. Using the distance formula, find which of them is correct.
| Case No. | Lens | Focal Length | Object Distance |
|---|---|---|---|
| 1 | \(A\) | 50 cm | 25 cm |
| 2 | B | 20 cm | 60 cm |
| 3 | C | 15 cm | 30 cm |