differentiation

[silk mountain]

for part b, why is the gradient of the normal equal to dy/dx at point P?
i thought we could only equate the negative reciprocal of the normal with the gradient at P?
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[small shell]

yh it should be the negative reciprocal of the gradient of the normal

[silk mountain]

but they equated them without finding the negative reciprocal

[small shell]

thats wrong