2.51 × 2.51 + 1.31 × 1.31 − 2.62 × 2.51 =

1. 1.44

2. 0.44

3. 1

4. 0

The value of ab if 3a + 5b = 15 and 9a² + 25b² = 75 is :

1. 4

2. 5

3. 6

4. 8

If l + m − n = 9 and l² + m² + n² = 31, then mn + nl − lm is :

1. -25

2. 25

3. -2

4. -5