Pls solve Q19

Pls solve Q19 16. 9x2 + 3x— 8y — 64y2 17. 9 1 (2a — 18. — (a + — ¯ 16 4 19. 2(ab + cd) — a2 — b2 + c2 + d2 20. Find the value of : (i) (987)2 - (13)2

It is given that a^2+b^2-c^2-d^2+2ab rearrange the terms =a^2+b^2+2ab-c^2-d^2-2cd =(a^2+b^2+2ab)-(c^2+d^2+2cd) =(a+b)^2-(c+d)^2 =[(a+b+c+d)] [(a+b)-(c+d)] =(a+b+c+d) (a+b-c-d) I hope this helps you