If the lines y=3x+1 and 2y=x+3 are equally inclined to the line y=mx+4, find the value of m.
Let θ be the angle which the line y=mx+4 makes with the lines y=3x+1 and 2y=x+3. Then
∴ tan θ=∣∣m−31+3m∣∣
and tan θ=∣∣∣m−121+m2∣∣∣=∣∣2m−12+m∣∣
⇒ ∣∣m−31+3m∣∣=∣∣2m−12+m∣∣
⇒ ∣∣m−31+3m∣∣=±∣∣2m−1m+2∣∣
⇒ m2−m−6=±(6m2−m−1)
⇒ 5m2+5=0 or 7m2−2m−7=0
⇒ m=1±5√27