Solve a linear equation
Find x in an equation like 3x + 5 = 20.
A linear equation has x only to the first power. Here 3x + 5 = 20. Take 5 from both sides to get 3x = 15, then divide by 3 to get x = 5.
Several calculators can do this for you with a solver. RPN calculators follow the same two steps by hand.
Classic Graphing 84 · Using the equation solver
Start on the main screen: Press 2nd then mode (QUIT) to get back to the home screen. Pressing clear on a menu also backs out of it.
Press MATH and go up to the last item, Solver. Press enter. The calculator wants an expression that equals 0.
math▲enterType 3X + 5 − 20 (move everything to one side) and press enter.
3X,T,θ,n+5−20enterPress alpha then enter (the SOLVE function). The answer appears on the X line.
alphaSOLVEenter
You should see3X+5−20=0 X=5
Classic Graphing 84 key reference · Classic Graphing 84 manual
Natural Scientific 991
Start on the main screen: Press MENU, then 1 (Calculate) to return to the main calculation screen. AC clears the line you are on.
Type 3x + 5, press ALPHA then CALC for the = sign, and type 20.
3ALPHAx)+5ALPHA=CALC20Press SHIFT then CALC (SOLVE). The calculator asks for a starting guess for x. Type 0 and press =.
SHIFTSOLVECALC0=
You should see3x+5=20 x=5
Natural Scientific 991 key reference · Natural Scientific 991 manual
Classic CAS
Start on the main screen: Press home to open the Home menu (Calculator, Graphs, Settings, and more). Choose Calculator, or press esc to go back to the calculation page.
Press menu, then 3 for Algebra and 1 for solve(. Type the equation 3x + 5 = 20, then a comma and x.
menu313x+5=20,x)Press enter.
enter
You should seesolve(3x+5=20,x) x=5
RPN Scientific 15 · By hand with the stack
Start on the main screen: There is no menu to leave. Press the back arrow to clear a number you are typing, or CLx (g then back arrow) to clear the X register.
Take 5 away from both sides: key in 20, ENTER, 5, then press −.
20ENTER5−Divide by the number in front of x: key in 3 and press ÷.
3÷
You should see5.0000
Tips
- Move every term to one side so the solver is looking for a zero. The sign matters: 3x + 5 = 20 becomes 3x + 5 − 20 = 0.
Related guides
- Solve a quadratic equationFind the roots of x² − 5x + 6 = 0 with a polynomial solver or the quadratic formula.
- Solve a system of two equationsFind x and y when 2x + y = 5 and x − y = 1.
- Solve an equation numericallyFind a root of any equation by giving a starting guess and letting the calculator home in on the answer.