Grade Assignment week 3 Wrong marking in Q11 and 13

[Inquisitive Learner]

Find the values of r for which the line (r+5)x–(r–1)y+r^2+4r−5=0 is  

Q. 11.  parallel to the x-axis

 is 1 not -5 as for line to be parallel to x-axis, coefficient of y should be zero!

Q. 13. parallel to the y-axis

is -5 not 1 as for line to be parallel to y-axis, coefficient of x should be zero!

This question is similar to a question in class XI RS Aggarwal, which confirms my logic. I'm attaching a snapshot from the book. 

[Anusha Murali Krishna]

Hi,

11. Coefficient of x has to be zero, if the line is parallel to x axis, as y= c. So (0)x+y=c.

Therefore r+5=0=> r=-5.

13. Same way coefficient of y has to be zero for the slope to be undefined (line parallel to y axis)

r-1=0,

r=1.

Hope this helps.

Anusha

[subhajit POD]

Thanks Anusha for the solutions. For the second part it is enough to write that, for a st. line to be parallel to Y axis, the coefficient of y should be 0, which eventually gives you that the slope is undefined. 

Best

Subhajit