Error in combining plots

I have two plots I1 and I2 for two different lines perpendicular to each other. When I combine these graphs they do not perpendicular to each other.

I1 = Plot[{-4 (x - 1) + 13}, {x, -1, 3}];
I2 = Plot[{(x - 1)/4 + 13}, {x, -1, 3}];
Show[I1,I2]

• mathematica 11.1, but I also checked in MA 10, it was giving same result. – m. bubu Aug 2 '17 at 14:34
• This is do to the rescaling to the axis of the fist graph, this is the default behaviour. i.e., not an error but a feature – Ruud3.1415 Aug 2 '17 at 14:42
• @Ruud3.1415 I understand this is due to scaling different . Actually my two lines are perpendicular to each other . I want to show this in plot but due to scaling problem these are not perpendicular to each other – m. bubu Aug 2 '17 at 14:59
• you do know that you can plot two lines at the same time? Plot[{-4 (x - 1) + 13, (x - 1)/4 + 13}, {x, -1, 3}, AspectRatio -> Automatic] – Ruud3.1415 Aug 2 '17 at 15:36

I1 = Plot[{-4 (x - 1) + 13}, {x, -1, 3}, AspectRatio -> Automatic]