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Mathematics · Ch 4 — Inverse Trigonometric Functions

Graph of the Inverse Sine Function

4.3.4

Graph of the Inverse Sine Function

sin⁡−1:[−1,1]→[−π2,π2]\sin^{-1}:[-1,1]\to\left[-\tfrac{\pi}2,\tfrac{\pi}2\right] receives x∈[−1,1]x\in[-1,1] and returns y∈[−π2,π2]y\in\left[-\tfrac{\pi}2,\tfrac{\pi}2\right]. As xx increases from −1-1 to 11, yy increases from −π2-\tfrac{\pi}2 to π2\tfrac{\pi}2; connecting the plotted points (x,y)(x,y) with a smooth curve produces Fig. 4.6.

Equivalently, Fig. 4.6 is obtained by reflecting the restricted sine curve of Fig. 4.7 (on [−π2,π2]\left[-\tfrac{\pi}2,\tfrac{\pi}2\right]) in the line y=xy=x — interchanging its xx- and yy-axes, as shown against the reflection line in Fig. 4.8. The graph passes through the origin and is symmetric about the origin, confirming once more that y=sin⁡−1xy=\sin^{-1}x is an odd function. …

Figure 4.6Graph of $y=\sin^{-1}x$, $x\in[-1,1]$

What this figure shows. A rising S-shaped curve through the origin, flattest at the centre and steepening near the endpoints, running from (−1,−π/2)\left(-1,-\pi/2\right) to (1,π/2)\left(1,\pi/2\right). …

Figure 4.7Restricted sine curve, $y=\sin x$ on $\left[-\pi/2,\pi/2\right]$

What this figure shows. The single monotonically increasing arch of sine used to build the inverse, from (−π/2,−1)\left(-\pi/2,-1\right) through the origin to (π/2,1)\left(\pi/2,1\right). …

Figure 4.8Restricted sine and the mirror line

What this figure shows. The Fig. 4.7 arch shown together with the diagonal y=xy=x that the inverse is reflected across. …

Figure 4.9Sine and inverse sine superimposed

What this figure shows. Both y=sin⁡xy=\sin x (restricted) and y=sin⁡−1xy=\sin^{-1}x drawn on one pair of axes together with the line y=xy=x, visually confirming each is the other's mirror image. …