**In ∆PQR, PD ⊥ QR, such that D lies on QR. If PQ = a, PR = b, QD = c and DR = d, prove that (a + b) (a – b) = (c + d) (c – d).**

**Solution:**

**More Solutions:**

- Find the altitude on BC and Hence, calculate its area.
- Find the area and the perimeter.
- Calculate the length of AB.
- Calculate the length of BD.
- Prove that AB2 = 4AD² – 3AC².
- The area of ∆ ABC is 60 cm². Find x.
- If diagonals are 30 cm and 40 cm.
- Find the area and perimeter of EFGH.
- Prove that 4AD² = 3AB².
- BC and CA respectively of a ΔABC.