I've got a casio fx 991plus calculator and I want to know how to use feet and inches in the calculation displays, like how is used meters and centimetres in the display

SOURCE: Inputing factors on a casio fx-115es calculator

Unless I am failing to understand your problem, just combine like terms to get:
9x^2+2x+4 and then enter those coefficients into the quadratic solver.
That will get you the two answers -- both of them will be complex.
If you wanted to turn those two answers into factors (complex) of the original equation simply
change the signs on each and put an x in front.
Of course, the quadratic formula would also work.
CG

SOURCE: m mod n in Casio fx991MS

there is one button ab/c beneath CALC... if u want to calculate 7 mod 4 then... u should press 7 then ab/c 4 and equal to
1, 3 ,4 which is 4*1=4 and 7-4=3 remainder...

SOURCE: Hi, I have a Casio calculator fx-991MS giving me wrong answers!

Hello,
I am only looking for a plausible cause of the error, because I do not believe your calculator can make such a mistake. I think you accidentally activated the Exponential display format and did not pay attention to the small, raised -03 that came at the end of the number displayed. It is a common mistake for those not very familiar with Scientific or exponential notation.

Let us try to reset your calculator to the normal (floating point) format.
Press the [MODE] key a number of times until you reach a screen that has FIX, SCI, NORM and under each one a number (FIX 1, SCI 2), Norm 3). To have the number of decimal place you gave in your result (4 decimal digits), you press 1 to select Fix then 4.

Be aware that scientific calculators usually stop displaying results in floating point format ( 0.0000045 ) if the number is smaller then 0.001. So basically, 0.00099 will be displayed as 9.90-04, -04 being raised above the level, and in smaller size.

Hope it helps.

Testimonial: "Thanks so much, its working now:) I thought I was going to have to buy a new calculator!"

SOURCE: Setting the default value of my calculator to display decimals

Hello,
Since you bent on deactivating the very features that make your calculator so versatile and so powerful, here it is.
Press [SHIFT][MODE][2:LineIO] and you will see no more fractions, nor radicals etc. You asked for it.
Hope it helps.

Testimonial: "I bought the calculator because it was on sale and I like Casio calculators; not for its fractional abilities. I can easily switch it back now. Thanks"

SOURCE: casio fx-82es significant figures

it should...

it can be found by SHIFT then MODE then SCI is the one you want to choose