Browse Questions

# Suppose $\overrightarrow {a}= \lambda \overrightarrow {i}- 7 \overrightarrow {j}+3 \overrightarrow {k}, \overrightarrow {b}= \lambda \overrightarrow {i}+\overrightarrow {j}+2 \lambda \overrightarrow {k}$. If the angle between $\overrightarrow {a}$ and $\overrightarrow {b}$ is greater than $90^{\circ},$ then $\lambda$ satisfies the inequality:

$\begin {array} {1 1} (1)\;-7 < \lambda < 1 & \quad (2)\;\lambda > 1 \\ (3)\;1 < \lambda < 7 & \quad (4)\;-5 < \lambda < 1 \end {array}$

$(1)\;-7 < \lambda < 1$
edited Jan 2, 2014 by meena.p