QUESTION IMAGE
Question
build perseverance find the coordinates of point l so △jkl is a right triangle. point j has coordinates (0, 0), and point k has coordinates (2a, 2b).
Step1: Analyze right triangle cases
A right triangle can have the right angle at \( J \), \( K \), or \( L \).
- Case 1: Right angle at \( J(0,0) \)
If \( \angle J = 90^\circ \), then \( JL \) is vertical/horizontal and \( JK \) is the other leg. Since \( J(0,0) \) and \( K(2a,2b) \), a perpendicular line at \( J \) could be along the x - axis or y - axis. A simple choice is \( L(2a,0) \) (here, \( JL \) is horizontal (\( y = 0 \)) and \( JK \) has slope \( \frac{2b - 0}{2a - 0}=\frac{b}{a} \), and \( JL \) has slope \( 0 \), \( JK \) and \( JL \) are perpendicular when \( a
eq0 \); or \( L(0,2b) \) (similar logic with vertical line)). Let's take \( L(2a,0) \) for simplicity. We can verify the slopes: slope of \( JK=\frac{2b - 0}{2a - 0}=\frac{b}{a} \), slope of \( JL=\frac{0 - 0}{2a - 0}=0 \), slope of \( KL=\frac{0 - 2b}{2a - 2a} \) (undefined, but actually, when \( L(2a,0) \), \( JL \) is horizontal, \( JK \) is a line from \( (0,0) \) to \( (2a,2b) \), and \( KL \) is vertical. The product of slopes of \( JL \) (slope \( 0 \)) and \( JK \) (slope \( \frac{b}{a} \)) is \( 0\times\frac{b}{a} = 0\), but actually, for right angle at \( J \), the vectors \( \overrightarrow{JJ}=(0,0) \) (no, better to use vectors \( \overrightarrow{JL}=(x, y) \) and \( \overrightarrow{JK}=(2a,2b) \). Their dot product should be zero: \( \overrightarrow{JL}\cdot\overrightarrow{JK}=2a\times x+2b\times y = 0 \). If we take \( x = 2a \), \( y = 0 \), then \( 2a\times2a+2b\times0 = 4a^{2}=0 \) only if \( a = 0 \), which is not general. Wait, maybe a better approach:
- Case 2: Right angle at \( K(2a,2b) \)
Vectors \( \overrightarrow{KJ}=(- 2a,-2b) \) and \( \overrightarrow{KL}=(x - 2a,y - 2b) \). Their dot product should be zero: \( - 2a(x - 2a)-2b(y - 2b)=0\Rightarrow - 2ax + 4a^{2}-2by + 4b^{2}=0\Rightarrow ax+by=2a^{2}+2b^{2} \). A simple solution is \( L(0,2b) \): check dot product \( \overrightarrow{KJ}=(-2a,-2b) \), \( \overrightarrow{KL}=(-2a,0) \), dot product \( (-2a)\times(-2a)+(-2b)\times0 = 4a^{2}
eq0 \) (wrong). Wait, maybe the easiest cases are when \( L \) is such that either \( JL \) is horizontal and \( KL \) is vertical or vice - versa.
- Case 3: Right angle at \( L \)
Let \( L=(x,y) \). Then \( \overrightarrow{JL}=(x,y) \), \( \overrightarrow{KL}=(x - 2a,y - 2b) \), and \( \overrightarrow{JK}=(2a,2b) \). For right angle at \( L \), \( \overrightarrow{JL}\cdot\overrightarrow{KL}=0\Rightarrow x(x - 2a)+y(y - 2b)=0 \). But the simplest non - trivial cases are when \( L \) is \( (2a,0) \) or \( (0,2b) \) (right angle at \( K \) or \( J \) respectively). Let's take \( L=(2a,0) \):
- \( J(0,0) \), \( K(2a,2b) \), \( L(2a,0) \)
- Length of \( JL=\sqrt{(2a - 0)^{2}+(0 - 0)^{2}} = 2|a| \)
- Length of \( KL=\sqrt{(2a - 2a)^{2}+(0 - 2b)^{2}} = 2|b| \)
- Length of \( JK=\sqrt{(2a - 0)^{2}+(2b - 0)^{2}} = 2\sqrt{a^{2}+b^{2}} \)
- Check Pythagoras: \( JL^{2}+KL^{2}=(2a)^{2}+(2b)^{2}=4a^{2}+4b^{2} \), and \( JK^{2}=(2\sqrt{a^{2}+b^{2}})^{2}=4(a^{2}+b^{2}) \). So \( JL^{2}+KL^{2}=JK^{2} \), so \( \triangle JKL \) is right - angled at \( L \).
Another simple solution is \( L=(0,2b) \). Let's verify:
- \( J(0,0) \), \( K(2a,2b) \), \( L(0,2b) \)
- \( JL=\sqrt{(0 - 0)^{2}+(2b - 0)^{2}} = 2|b| \)
- \( KL=\sqrt{(0 - 2a)^{2}+(2b - 2b)^{2}} = 2|a| \)
- \( JK = 2\sqrt{a^{2}+b^{2}} \)
- \( JL^{2}+KL^{2}=4b^{2}+4a^{2}=JK^{2} \), so it is also a right triangle.
Step2: Conclusion
One of the possible coordinates of \( L \) is \( (2a,0) \) (or \( (0,2b) \)). We will take \( (2a,0) \) as a valid solution (other solutions like \( (0,…
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\((2a,0)\) (or \((0,2b)\) is also a valid answer)