Strike of limestone bed directed N20°E, dip 45°

The strike is the direction of the horizontal line on the bed and it is always at 90° to the dip direction.

Given: Limestone bed directed (dipping) towards N20°E with a dip of 45°. Dip direction = N20°E, azimuth = 20°.

$$\begin{aligned} \text{Strike} &= \text{dip direction} \pm 90° \\ &= 20° - 90° = 290° \ \text{or}\ 20° + 90° = 110° \end{aligned}$$

These two azimuths (290° and 110°) are the two ends of one line, so the strike is N70°W (S70°E).

                    N
         N70W \     |     / dip N20E
                \   |   /
                  \ | /
  W ----------------+--------------------- E
                    | \
                    |   \
                    |     \ S70E
                    S
   ( \ = strike line N70W-S70E,  / = dip direction N20E, at 90 deg to strike )

Answer: Strike = N70°W (S70°E).